1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device which method involves using a solution containing a perhydrosilazane polymer to form an insulating film containing silicon and oxygen.
2. Description of the Related Art
A reduction in the size of LSIs is intended to increase the components per chip to improve the performance of devices (for example, an increase in operating speed and a reduction in power consumption) and to reduce manufacture costs. The recent minimum design rule is nearly 0.1 micron on a mass production level. A further reduction in the size of LSIs is difficult but the design rule is expected to be further reduced to 0.1 micron or less in the future. A Logic device of gate length as small as about 30 nm has been produced at the experimental stage.
To increase the components per chip, it is important to reduce the size of isolation areas that occupy most of the element area. In recent years, an STI (Shallow Trench Isolation) technique has been adopted as a method of forming very small isolation areas. The STI technique forms an isolation area by filling an insulating film (isolation insulating film) into a trench (isolation trench) formed by anisotropic etching.
The STI technique has realized an isolation region with a trench of width about 90 to 70 nm, which corresponds to a minimum machining dimension of at most 0.1 micron. For memories, which require the highest components density, the width of an active area for a transistor or an isolation area has recently been nearly 90 to 70 nm, which corresponds to a minimum machining dimension of at most 0.1 micron. Accordingly, a reduction in the size of the memory isolation area has also become important.
The difficulty in the formation of an isolation area has been increasing with decreasing LSI size. The reason is as follows. The capability of separating elements from each other is determined by the effective distance between adjacent elements. The effective distance is determined by the minimum distance of peripheral length of the isolation trench from one of its sidewalls through its bottom surface to the other sidewall. To avoid degrading the isolation capability in spite of a reduction in the size of devices, it is necessary to keep the effective distance at least a conventional value, that is, to almost fix the depth of the isolation trench. The width of the isolation trench decreases consistently with the LSI size. The aspect ratio of the isolation trench increases with progression of the generation of size reduction. This causes the difficulty in the formation of an isolation area to increase with decreasing LSI size.
A high density plasma (HDP) CVD process is a currently standard technique for forming an isolation insulating film. If the HDP-CVD process is used to form a silicon oxide film (HDP silicon oxide film) in an isolation trench of the 0.1 micron generation or earlier, the aspect ratio reaches at least 3. It is thus very difficult to form an HDP silicon oxide film free from a void (unfilled part), in the isolation trench. The presence of a void in the HDP silicon oxide film in the isolation trench may degrade insulating properties.
A currently promising technique for filling a very small isolation trench is a method of filling the isolation trench with a spin on glass (SOG) film formed by a spin coating method or a flowable insulating film such as an O3/TEOS film or a method of filling the isolation trench with the conventional HDP silicon oxide film and the flowable insulating film.
A known filling technique using the flowable insulating film is a method of coating a solution containing a perhydrosilazane polymer (polysilazane) on a silicon substrate in which isolation trenches are formed, filling the polysilazane film into the isolation trenches, and then using a diffusion furnace to heat the polysilazane film in a water vapor atmosphere to convert the polysilazane film into a silicon oxide film (Jpn. Pat. Appln. KOKAI Publication Nos. 2004-179614 and 2002-367980).
Impurities remain in the silicon oxide film formed by the above method; the impurities include nitrogen (N) contained in the material and carbon (C) contained in an organic solvent such as dibutylether. The impurities remaining in the silicon oxide film act as plus fixed charges. The fixed charges may degrade the insulating properties of the silicon oxide film.